A delay line deflection structure is a deflection apparatus of the traveling wave type used in cathode ray tubes for high frequency oscilloscopes to reduce the magnitude of deflection signal velocity in the direction of the travel of electrons in the electron beam. Traveling wave delay line deflection structures generally comprise a pair of deflection members disposed on opposite sides of and extending along the path of an electron beam. An electric field varying in intensity and direction in accordance with the magnitude and polarity of the deflection signal deflects the electron beam. A delay is introduced to reduce the speed of deflection signal propagation along the deflection structure until it equals the speed of the beam electrons, thereby allowing accurate beam deflection with very high frequency signals.
Parameters governing signal delay include (1) the lengths of the delay line lead portions interconnecting deflection elements extending transversely of and distributed along the path of the electron beam and (2) the effective values of the distributed inductance and capacitance components, which affect the speed of wave propagation along the line. The precise nature and value of the component impedances depend upon the particular design of delay line structure. A delay line deflection structure of the traveling wave type is a transmission line having a characteristic impedance, which is defined as the apparent impedance of an infinitely long transmission line at any point. Terminating a transmission line of finite length with an impedance having a value equal to its uniform characteristic impedance produces a line simulating a transmission line of infinite length and prevents signal reflections from the termination impedance that tend to produce signal wave form distortion.
The characteristic impedance of a delay line deflection structure is an aggregate of the intricately related, complex impedance components distributed along the length of the line. These include primarily the inductance per unit length and the capacitance per unit length between the line and the member serving as the ground electrode or plane. Inductance is directly proportional to the spacing between the line and the ground plane and is inversely proportional to the width of the line. Capacitance is inversely proportional to the spacing between the line and the ground plane and is directly proportional to the width of the line. The capacitance between adjacent deflection elements of the delay line and the capacitance between adjacent lead portions interconnecting these elements also materially affect the characteristic impedance.
Delay line deflection apparatus generally include meander line and helical deflection structures. By virtue of its design, a helical deflection structure has an inherent capability of providing characteristic impedances exceeding those obtainable in meander line deflection structures. Helical deflection structures are, however, more expensive to manufacture and difficult to assemble.
Maintaining a substantially uniform impedance along the length of a transmission line is necessary to prevent reflection of the deflection signal back toward the input end. In addition, a transmission line type electron beam deflector with a high characteristic impedance reduces the load on, and thereby the current drawn from, the vertical amplifier driving the electron beam deflector in a cathode ray oscilloscope. A high load impedance is beneficial in enhancing the deflection sensitivity of the oscilloscope, reducing amplifier power consumption, simplifying heat sinking requirements for active semiconductor devices, and permitting the use of power transistors of less sophisticated design.
Certain deflection structures are adapted to be driven by the output of a single-ended vertical amplifier. In deflection structures of this type, the deflection signal is applied to a single deflection member to vary the intensity and direction of the electric field between the deflection member and a ground plane positioned on the opposite side of the beam from such deflection member.
Other deflection structures have been designed to be driven by the output of a double-ended vertical amplifier operating in a push-pull configuration. These push-pull deflection structures heretofore have comprised a pair of identical deflection members, each connected to an output of the vertical amplifier. Vertical deflection signal voltages of opposite phase are produced by the push-pull vertical amplifier. These vertical deflection signals propagate along the deflection members at the same speed as that of the electrons in the electron beam to vary the intensity of the electric field between the deflection members. Each deflection member serves as the ground plane for the other. The push-pull arrangement effectively doubles the deflection field intensity by applying an equal, but oppositely phased deflection signal voltage to the second deflection member to double the potential difference between the two deflection members.
Delay line type deflection structures have been disclosed heretofore for use in high frequency oscilloscope cathode ray tubes. Thus, U.S. Pat. No. 2,922,074 of Moulton issued Jan. 19, 1960, discloses a meander line type deflection structure having an elongated slotted flat deflection plate disposed face-to-face between a pair of similar flat ground plates. The slotted deflection plate, which is situated considerably closer to one of the ground plates than the other, has a plurality of narrow slots extending inwardly alternately from opposite edges thereof. The inner ends of the slots overlap to provide laterally extending conductive elements which extend transversely of the beam of electrons and provide a zigzag meander line path for a vertical deflection signal propagated along the deflection plate from the inlet end to the outlet end thereof.
The characteristic impedance of the deflection structure described in the Moulton '074 patent is changed by varying its distributed inductance and capacitance. The inductance per unit length can be changed by varying the length and width of the slots in the deflection plate, thereby changing the spacing between adjacent conductive elements of the meander line but preserving a uniform number of conductive elements per unit length along the deflection plate. The number of conductive elements per unit length is referred to as pitch. The capacitance per unit length can be changed by varying the width of the deflection plate and of the ground plates on either side thereof, and by varying the distance between the deflection plate and the nearer ground plate.
Although the Moulton '074 patent meander line deflector was disclosed with reference to a single deflection plate driven by the output of a single-ended vertical amplifier, it was suggested that a deflection structure of the push-pull type having a second identical deflection plate could be driven by a double-ended output, push-pull type vertical amplifier. Unlike the two deflection members of the present invention, however, such pair of deflection plates would both be of the same pitch.
Unlike the present invention, the Moulton '074 patent meander line deflector comprises a complex, multilayered delay line structure including a single deflection plate having a constant pitch to achieve the characteristic impedance. For operation in a push-pull configuration, a second identical deflection plate is added within the structure for positioning in accordance with a complex alignment procedure.
U.S. Pat. No. 3,174,070 of Moulton issued Mar. 16, 1965, discloses a deflection structure similar to that described in the Moulton '074 patent, but a portion of one ground plate is replaced by a short section of zigzag deflection plate to provide a compensation means for improving high frequency and transient signal response. A deflection structure of this type cannot be driven by the output of a double-ended, push-pull vertical amplifier.
U.S. Pat. No. 3,504,222 of Fukushima issued Mar. 31, 1970, describes several embodiments of delay line deflection structures that include a meander line of conducting material in the form of a flat serpentine strip. The characteristic impedance of the meander line is adjusted by interposing grounded shield members between the pitch intervals in the meander line strip. The shield members alter the capacitance between adjacent meander line elements to improve the dispersion characteristics of the deflection structure. In addition, Fukushima discloses the use of tapered sections within the meander line structure to alter the impedances thereof.
Each embodiment disclosed in Fukushima is a single meander line structure spaced from a ground plate, thereby rendering each embodiment suitable as an output load for only a single-ended vertical amplifier. At least one embodiment is shown having the meader line member and the opposed ground plate curving outwardly to provide a flared-apart space at the output end of the deflection structure. The flared output section provides clearance for deflection of the electron beam and raises the impedance of the deflection structure near the output end thereof. In all embodiments, the pitch is held constant along the entire length of the meander line member. There is no disclosure of pitch compensation or any other means to accomplish a uniform characteristic impedance by compensating for the increased impedance at one end due to the flared spacing between deflection members.
U.S. Pat. No. 4,207,492 of Tomison, et al. issued June 10, 1980, describes an electron beam deflection structure for a high frequency cathode ray tube incorporating a meander line delay line structure. The deflection system includes an opposed pair of identical deflection members each comprising a serpentine meander line having a series of U-shaped loops formed by a pair of interconnected lead portions. Each lead portion is connected to a deflection plate segment of greater width along the beam path. The deflection members flare apart approximately one-third the way down the length of the deflection structure toward the output end and are adapted to be driven by a double-ended, push-pull vertical amplifier.
For each deflection member of Tomison, et al., the radii of curvature of the U-shaped loops situated near the output end are greater than those of the U-shaped loops near the input end. This produces a non-constant pitch along the length of each deflection member. Since the deflection members are identical, the pitch of each changes in the same manner along the length thereof to provide a symmetrical deflection structure having a non-constant pitch. The change in pitch along the length of the deflection structure compensates for the change in impedance due to the increased separation between the deflection members at the flared-apart output end. The increased pitch at the input end of the deflection member increases the impedance to make more uniform the impedance along the length of each line.
The deflection structure disclosed in Tomison, et al. differs from the present invention in that the former includes a symmetrical deflection structure having two identical deflection members, each with a nonuniform pitch to compensate for the increasing impedance produced by the flaring apart at the output ends.
U.S. Pat. No. Re 28,223 of Odenthal, et al. issued Nov. 5, 1974, describes a delay line deflection structure comprised of a pair of helical deflection members with rectangular turns, each having a pair of flat side lead portions connected to a deflector portion of greater width. The deflection members flare apart approximately one-half the way down the length of the deflection structure toward the output end. The width in the beam direction of the side lead portions increases successively along the path of the electron beam to help provide a uniform characteristic impedance by compensating for the increasing impedance due to the divergence of the helical deflectors.
The deflection structure also includes two pairs of grounded, adjustable compensator plates which are positioned adjacent the flat side portions on opposite sides of both helical members to form delay lines of substantially uniform characteristic impedance.
The spacing between side portions of adjacent turns of the helical structure successively decreases along the path of the electron beam, thereby preserving a substantially uniform pitch along the entire length of the deflection member. The width of and the spacing between adjacent deflector portions remain substantially constant along the entire length of each deflection member.
Unlike the present invention, the deflection structure disclosed by Odenthal, et al. is a symmetrical deflection structure comprised of a pair of identical deflection members having the same constant pitch. In addition, adjustable compensation plates are required to tune the impedance of the line.
U.S. Pat. No. 4,093,891 of Christie, et al. issued June 6, 1978, discloses a helical deflection apparatus similar to that disclosed by Odenthal, et al. Christie describes a helical deflection structure including two identical helix deflection members, each having a substantially uniform pitch along the length thereof. The adjustable compensator plates described by Odenthal, et al. are replaced by a ground plane folded into a rectangular channel and inserted into each rectangular helix deflection member.
That the impedance of a transmission line can be increased in a meander line structure comprising an insulator plate, such as a printed circuit board, carrying on opposite sides thereof two closely coupled meander lines meandering in opposite directions and having identical constant pitches was known to the inventor prior to his invention of the deflection structure disclosed herein. The present invention differs from this by employing a pair of closely coupled delay line type deflection members having different pitches that not only provide an overall increase in the characteristic impedance for the deflection structure, but also compensate for the changing impedance due to a flared-apart spacing between deflection members thereby to maintain a substantially constant characteristic impedance.